During the rolling, the rolling rod thereby supports itself against a mandrel thrust block with its end that faces away from the mandrel. A solid and mostly round metal block that is heated to rolling heat, is pierced and is stretched in the further process to form a seamless pipe. The hole is hereby created in that the round block is driven by the rollers that are set at an angle, and is rolled via a mandrel. It is thereby the object of the mandrel to pierce the core zone of the block, to smooth the inner surface of the created hollow block and to bring the wall thickness thereof to the desired measure.
Such a method as well as a device for carrying out the method is known from DE 1 96 04 969 C2, for example. This publication deals in particular with the wear of the forming tools and the necessity to cool them as well with the impact of the coolant on the rolling stock itself.
When the heated metal block is in contact with the atmospheric oxygen or oxygen from other sources, such as the cooling water, for instance, scale, which must ideally be detached prior to the further forming, but no later than during the forming so as to prevent surface errors at the inner surface of the finally created seamless pipe, are created at the inner surface of the hollow block and also in deforming steps that follow the first forming process, if necessary.
Prior to the further forming of the hollow block into a seamless pipe, the method that is typically used for this provides for the blow-off of already loosened scale by nitrogen or air as is well as for the subsequent introduction of borate-containing powders, such as borax, for example. For the most part, this borax melts on the surface of the hollow block, loosens the scale to the extent that it can be blown out of the interior of the hollow block reliably and converts the scale into a liquid form. The introduction of the borate-containing powders takes 4 to 10 seconds. Finally, the discharge, which may be necessary, of the scale that has been softened, liquefied or loosened by the borate-containing powder, requires an additional 1 to 8 seconds.
The methods known from the state of the art thus not only result in an undesired delay of the production process as a whole, but also to a considerable discharge of borax and the burn-off thereof into the environment, due to the use of typically approximately 2 kg of borax for each ton of rolling stock. Finally, the temperature of the hollow block is also lowered in an undesirable manner by this method step that was required until now.
To overcome the interfering influences of the mill scale downstream from the piercing process, JP 63-154207A additionally proposes the introduction of a lubricant made of graphite into the area between an elongator mandrel and the inner surface of the hollow block. The formation of scale, however, is not significantly prevented by this.